Need help with email repair!

After doing too much registry cleaning, I now have a problem with my email client.
I use Yahoo Mail.
When I am on a web site and try to click on an email link so as to send an email, the [attached] "warning" window pops up! Does anyone know if this can be repaired?
trying to get help from Yahoo Support is a waste of time because you can never talk to a person.
Any advice would be appreciated but please, if explaining what I should do and how to do it, please explain in "layman's" terms.
Thank you.

actually, yahoo/gmail are not email clients -- they're webmail clients

(what attachment?)
Has it ever worked that way? -- I doubt it.
most website links for "send email" invoke a mailto:someone@website-domain
which will invoke your default email client -- which is undefined.

I believe you need to copy link,
log into your webbased email,
pase the link,
remove the mailto:
and then complete your msg and click send.